This invention relates to mechanical interval timers designed for domestic or household use. Such timers are employed in the kitchen and are usually intended to time intervals of between one and sixty minutes. Such timers are driven by a spring which is initially tensioned, and the prescribed time interval to be timed is set by simply rotating a pointer or index mechanism from zero to the desired number of minutes, which rotation further tensions the spring. This spring then drives, through a gear train, an escape wheel which is permitted to rotate at a controlled speed by an escape lever disc which oscillates in and out of obstructing relationship with the escape wheel. The escape wheel is a toothed member which rotates adjacent the escape lever disc. A pair of posts on the escape lever disc oscillate into and out of engagement with the teeth on the escape wheel thereby permitting the gear train to unwind until it returns to the zero setting at which time a bell is normally sounded.
It is well-known in the art to provide means for adjusting the rate of movement of the escape wheel by varying the distance between the axes of the escape wheel and the escape lever disc. As the distance between these axes is reduced, the escape wheel is caused to rotate more slowly and, conversely, when the distance is increased, the escape wheel rotates more rapidly.
It had been well-known in the prior art to provide one of the metallic frame members which supported the escape lever disc with a deformable portion which would permit repositioning the bearing for the escape lever disc in order to recalibrate the movement. This calibration was done on an individual basis for each movement.
It has become common in the timer art to utilize plastic gears rather than the stamped or die cast gears which had formerly been used. Although plastic gears can be dimensioned very accurately, there are variations resulting from different mold cavities and the like which tend to provide dimensional differences which were not common in the metal gears. Accordingly, there have been increased needs to calibrate timers which have been made with plastic gears. However, due to the intense price competition in the low-cost mechanical timer field, it is not feasible to calibrate each individual timer. By means of the method and apparatus of my invention, it is possible to produce an accurate low-cost interval timer without calibrating each individual unit.